The present invention relates to methods, systems and apparatus for transmitting data to and/or receiving data from mobile terminals in a wireless communications system.
Embodiments of the present invention can for example allocate transmission resources for, and transmit control data to, groups of machine type communication (MTC) devices in cellular telecommunications networks having orthogonal frequency division multiplex (OFDM) based radio access technology (such as WiMAX and LTE).
Certain classes of telecommunications device, such as MTC devices (e.g. semi-autonomous or autonomous wireless communication terminals), support “low capability” communication applications that are characterised, for instance, by the transmission of small amounts of data at relatively infrequent intervals. MTC devices are constructed so that individually they represent little burden on telecommunications networks and thus can be deployed in greater numbers than equivalent “full capability” terminals in the same networks.
In many scenarios, it is preferable to provide terminals dedicated to such “low capability” communication applications with a simple receiver unit (or transceiver unit) having capabilities more commensurate with the amount of data likely to be transmitted to (or from) the terminal. This more limited capability contrasts with the capabilities of the conventional mobile telecommunications terminals, such as smartphones, which share access to the same telecommunications networks.
To support MTC terminals, it has been proposed to introduce a “virtual carrier” operating within a bandwidth of one or more “host carriers”: the proposed virtual carrier concept preferably integrates within the transmission resources of conventional OFDM based radio access technologies and subdivides frequency spectrum in a similar manner to OFDM. Unlike data transmitted on a conventional OFDM type downlink carrier, data transmitted on the virtual carrier can be received and decoded without needing to process the full bandwidth of the downlink OFDM host carrier. Accordingly, data transmitted on the virtual carrier can be received and decoded using a reduced complexity receiver unit: with concomitant benefits such as reduced complexity, increased reliability, reduced form-factor and lower manufacturing cost.
The virtual carrier concept is described in a number of co-pending patent applications (including GB 1101970.0 [2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8 [6], GB 1101982.5 [7], GB 1101980.9 [8] and GB 1101972.6 [9]), the contents of which are incorporated herein by reference.
In one implementation of the virtual carrier (VC) concept, described in co-pending patent application GB 1121767.6 [11], VC capable MTC devices are presumed to receive only certain OFDM symbols across all host carrier (HC) sub-carriers (the HC control region)—the remaining OFDM symbols are typically received across one of a plurality of VC bandwidth ranges. The VC provides dedicated VC control regions amongst the symbols received across the VC bandwidth range.
In conventional LTE, at least some of the resource elements (REs) comprising this HC control region are defined by specification to form a number of so-called control channel elements (CCEs). A physical downlink control channel (PDCCH), for providing control information to devices, comprises a number of CCEs. The number of CCEs comprising a particular PDCCH depends on the aggregation level determined by the eNodeB (see later for discussion of aggregation levels). A UE must search through some number of the CCEs in the control region to determine if there are any that comprise PDCCHs containing control information pertinent to the UE. Some CCEs are searched by all UEs, these CCEs comprising a so-called common search space (CSS), and some CCEs are not searched by all UEs, these CCEs comprising a so-called UE-specific search space (UESS). A CCE may be part of more than one search space. Typically, PDCCHs comprising CCEs in the common search space contain information relevant to all UEs in a cell and PDCCHs comprising CCEs in a UE-specific search space contain information relevant only to one UE.
The HC control region has a limited number of REs and this limitation may restrict the number of MTC devices that may be deployed: since each MTC device requires a corresponding UESS. It is predicted that the number of MTC devices will increase markedly in the coming years and the limitation on REs in LTE can be expected to restrict many MTC scenarios.
An efficient operation of a wireless telecommunications system for MTC devices is therefore desirable.